(1) Field of the Invention
This invention relates to rotary pumps.
(2) Prior Art
Rubber impeller pumps are commonly used in marine and other applications because of their self-priming ability. This type of pump is found in almost every type of vessel afloat and has been blamed for more engine seizures and failures caused through engine overheating than any other component. The problem with this type of pump is the high friction in the pump due to the impeller vanes' continuous hard contact with the housing and its compression by the cam. The impeller vanes compressed by the cam between the inlet and exhaust ports act as a valve. Damage is also caused by "engine rolling" when a diesel engine stops.
This is caused by compression bouncing the pistons in reverse on stopping, causing the impellor to be turned in reverse. When the engine is started, the impeller is turned in the original direction. When the impeller vanes are turned over during the reversal of direction at least some of the vanes are pinched between the cam and the housing which eventually results in failure of the vane. The broken vanes reduce the capacity of the pump, can damage or break other vanes and can enter the engine block and block the flow causing overheating.
When started dry, the friction can rapidly destroy the impeller and both the impeller and housing are damaged by sand or mud in the water being pumped.
Despite the widespread use of such pumps, their failures are well known.